Ultrasonic technology has been applied to the fabrication of wire-reinforced plastic-wrapped tubing by a process wherein overlapped plies of a plastic wrapping are passed between a stationary anvil surface and an ultrasonic horn and fused together. Fusion is characteristically carried out over wide overlapping areas comprising as much as ninety percent of the tubing surface area. As fusion is taking place and the plastic is softened by heat and vulnerable to damage it is passed in sliding contact over a stationary anvil surface, and hence measures have to be taken to safeguard against tearing or stretching of the plastic. Among these are the use of particularly plastic films of more than one mil and slow production speeds of fifteen feet per minute of tubing or less. The resulting prior art product typically has a rather stiff-multi-ply wall of greater than 2.5 mil thickness.
The background of this invention also includes current practices for making air conditioning ducts, products to which the ultrasonic methods embodied herein are particularly suitable. Typical prior art air conditioning tubing consists of plastic tape wrapped with overlapping turns about plastic-coated steel wire and covered by thermal insulation and an outer moisture barrier. The plastic tape may be a continuous plastic film, and the above described conventional ultrasonic method has been used to make such a product. In other cases to improve sound deadening acoustical properties the continuous plastic film may be replaced by woven scrim fabric coated with plastic with overlapping turns joined by adhesive, all of which adds considerably to the cost of the product.
Finally, the background of the present invention includes well known apparatus and methods for making wire-reinforced flexible hose, such as those described in U.S. Pat. Nos. 2,486,387, 2,759,521, 3,219,733 and 3,336,172. It is known from that prior art to make tubing on a plurality of rotatable mandrels cantilevered from a frame with semi-circular wire-receiving grooves formed about the mandrels and spaced apart longitudinally depending upon the pitch desired in the wire helix. However, ultrasonic sealing has not previously been adapted to such tube-making concepts.